This image from the ChemCam instrument shows detailed texture of a rock target called "Elk" on Mars' Mount Sharp. Image Credit: NASA/JPL-Caltech/LANL/CNES/IRAP/LPGNantes/CNRS/IAS

In detective stories, as the plot thickens, an unexpected clue often delivers more questions than answers. In this case, the scene is a mountain on Mars. The clue: the chemical compound silica. Lots of silica. The sleuths: a savvy band of Earthbound researchers whose agent on Mars is NASA's laser-flashing, one-armed mobile laboratory, Curiosity.

The Curiosity rover has found much higher concentrations of silica at some sites it has investigated in the past seven months than anywhere else it has visited since landing on Mars 40 months ago. Silica makes up nine-tenths of the composition of some of the rocks. It is a rock-forming chemical combining the elements silicon and oxygen, commonly seen on Earth as quartz, but also in many other minerals.